Telephone system



Nov. 4, 1941. s. E. PETERSON ETAL 2,261,485

TELEPHONE SYSTEM Filed April 11, 1940 e Smeets-sheet 1 Nov. 4, 1941.s..E. PETERSON ETAL 2,261,485

TELEPHONE SYSTEM -Filed April 11, 1940 e sheets-sheet 3 Nov. 4, '1941.s. E. PETERSON E-r AL I 2,251,485

TELEPHONE SYSTEM Filed April 11, 1940 6 sheets-sneek 4 Quik@ QA .I

Mmmm

WQQ wml@ kmml xm E@ v iNvENToRS Y sETH E. PETERSON BY MoRRls-E.GR|FF|NsMIM, null :KU-MIE.

ATTORN EYS Nov. 4, 1941. s. PETERSON Erm.

n TELEPHONE 'SYSTEM e shefs-sheet 5 Filed AprilV ll, 1940 SETH E.PETERSON MORRIS E. GRIFFINS Mil MMR ATTORNEYS Nov. 4, 1941.

s. E. PETERSON ErAl.

. TELEPHONE SYS TEM Filed April4 l1, 1940 6 Sheets-Shea?I -6 INVENTORSSETH E. PETERSON MORRIS E. GRIFFINS ATTORNEYS Patented Nov. 4, 19412,261,485 TELEPnoNEsYsTEM Seth E. Peterson, Chicago, and Morris E.Griflins, Riverside, Ill., assigncrs to Associated ElectricLaboratories, Inc., Chicago, Ill., a corporationL of DelawareApplication April 11, 1940, Serial No. 329,086

43 Claims. (Cl. 179-27) The present invention relates to telephonesystems and more particularly to improvements in telephone systems ofthe semi-automatic type.

In a telephone system of the semi-automatic type a call initiated on atelephone line is automatically extended by associated switchingapparatus to an operator position to be answered; and after the call isanswered at the operator position, the operator thereat controls anassociated switch train to eXtend the call to the desired destination.In a telephone system of this character the switch train associated withthe operator position frequently comprises diierent types of automaticswitches, rendering it necessary for the operator to manipulatecorresponding different types of calling devices at the operatorposition in order to control the different types of automatic switchesin the associated switch train. As a result of this type of control, alarger number of errors is made and more delay is encountered at theoperator position in extending calls than is desirable.

Accordingly, it is an object of the present invention to provide in atelephone system of the type described comprising an operator positionand a switch train including a number of different types of automaticswitches, an improved unitary calling device at the operator positionwhich is operative selectively to control indiscriminately the differenttypes of automatic switches in the associated switch train,

Another object of the invention is to provide in a telephone system ofthe type described including an operator position, improved switchingapparatus for routing calls to the operator position to be answered.

Another object of the invention is to provide in a signaling system, animproved register arrangement for selectivelycontrolling the operationof an associated automatic'switch.

Another object of the invention is to provide in a signaling system, animproved register arrangement for selectively controlling the operationof an associated `repeater which is operative to repeat switch controlimpulses.

A further object of the invention is to provide in a signaling system,an improved repeater which is operative to repeat switch controlimpulses.

A further object of the invention is to provide in a signaling systemcomprising a repeater which is operative to repeat switch controlimpulses; an improved arrangement including an impulse generator forselectively controlling the operation of the repeater.

A further object of the invention is to provide in a signaling systemcomprising a number of repeaters each of which is operative to Arepeatswitch control impulses, an improved arrangement including an impulsegenerator commonly associated with the repeaters forselectivelycontrolling the operation of the repeaters A further objectof the invention is to provide in a signaling system, an improvedimpulse generator which is adapted to be utilized in a repeater network.

The features of the present invention are illustrated as beingincorporated `in ay telephone system comprising a centralexchange-'terminating a plurality of manual telephone lines and adistant exchange terminating a plurality of manual telephone lines, thecentral exchange and the distant exchange being interconnected by` twogroups of one-way trunk lines extending therebetween. The centralexchange comprises an operator switchboard provided with a vnumber ofoperator positions; and each exchange comprises an automatic switchtrain', the automatic switch train in the central exchange including'arepeater network.

In accordance with one feature of the invention the telephone systemcomprises a trunk including rst and second line conductors, switchingapparatus having access to the trunk, an automatic switch terminatingthe trunk, a plurality of lines accessible to the automaticvswitch,means for causing the automatic switching apparatus to seize thetrunk when the trunk is idle, means controlled by the seizure of thetrunk for impressing a predetermined potential upon the Yiirst lineconductor of the trunk, means controlled when the predeterminedpotential is impressed upon the :drst line conductor of the trunk forconditioning the automatic switch, and means controlled when theautomatic switch is conditioned for rendering busy the trunk. Also thesystem' comprises means for operating the automatic switch after it isconditioned, thereby to cause the automatic switch to seize one of thelines, and means for initiating the release of the automatic switch, theautomatic switch being so connected and arranged that it is adapted tobe completely released when the release thereof is initiated. Furtherthe system comprises means controlled in the event theautomatic switchfails completely to release for impressing a predetermined potentialupon the second line conductor of the trunk, and means controlled whenthe predetermined potential is impressed upon the second line conductorof the trunk for rendering busy the trunk Further the system comprises agiven telephone line associated with the switching apparatus, theswitching apparatus being operated in response to the presence of acalling condition upon the given telephone line to seize the trunk whenthe trunk is idle. Also the telephone system comprises an operatorposition, means controllable from the operator position for selectivelyoperating the automatic switch, the automatic switch being operative ina rst predetermined manner to seize one of the lines accessible theretoand in a second predetermined manner without seizing one oi the linesaccessible thereto, means included in the automatic switch andcontrolledby the operation thereof in the second manner for causing therelease of the automatic switch, and means controlled by the release ofthe automatic switch for rendering idle the trunk and for locking out ofservice the given telephone line in the event there is a callingcondition thereon.

In accordance with another feature of the invention the system comprisesa register, means for registering diierent digits in the register, anautomatic switch including a switching mechanism and an impulseresponsive motor for operating the switching mechanism and an impulsetransmitter operative to transmit impulses to the motor, means forconnecting the register to the switch, means for initiating operation ofthe impulse transmitter, means controlled revertively from'the switch inaccordance with the operation of the impulse transmitter to transmitimpulses to the motor for clearing the register of the digit registeredtherein, whereby the register is cleared of the digit registered thereinwhen the number of impulses transmitted from the impulse transmitter tothe motor corresponds to the digit registered in the register, and meanscontrolled when the register is cleared of the digit registered thereinfor arresting operation of the impulse transmitter. More particularly,the impulse transmitter in the switch is of the step-by-step type, theimpulse transmitter being operative to transmit a direct impulse to themotor and a revertive impulse to the register upon each step thereof;and the control arrangement for the impulse transmitter includes meansfor initiating step-by-step operation of the impulse transmitter, andmeans controlled when the number of revertive impulses transmitted fromthe impulse transmitter to the register corresponds to the digitregistered therein for arresting stepby-step operation of the impulsetransmitter.

In accordance with a further feature of the invention the systemcomprises a repeater including an impulse transmitter operative totransmit impulses from the repeater, means for connecting the registerto the repeater, means for initiating operation of the impulsetransmitter, means controlled revertively from the repeater inaccordance with the operation of the impulse transmitter for clearingthe register of the digit registered therein, whereby the register iscleared of the digit registered therein when the number of impulsestransmitted from the repeater corresponds to the digit registered in theregister, and means controlled when the register is cleared of the digitregistered therein for arresting operation of the impulse transmitter.More particularly, the transmitter in the repeater is operative totransmit switch control impulses and register control impulses at apredetermined rate and the arrangement for controlling the operation ofthe repeater includes means for initiating operation of the impulsetransmitter and means merges -controlled when the number of registercontrol impulses transmitted from the impulse transmitter to theregister corresponds to the digit registered therein for arrestingoperation of the impulse transmitter.

In accordance with a further feature of the invention the systemcomprises a number of registers, means for registering diil'erent digitsin the registers, switching means operative through a number of cyclessuccessively to connect and disconnect the registers and the repeater,the switching means being operative through a given cycle to connect agiven register to the repeater and then to disconnect the given registerfrom the repeater, the impulse transmitter included in the repeaterbeing operative through a cycle to transmit a series of switch controlimpulses, means for initiating a cycle of operation of the switchingmeans, means controlled when a register is connected to the repeater forinitiating a cycle of operation of the impulse transmitter, and meanscontrolled revertively from the repeater in accordance with theoperation" of the impulse transmitter for completing a cycle ofoperation of the switching means and then for initiating another cycleof operation of the switching means, whereupon one of the registers isdisconnected from the repeater and then another of the registers isconnected to the repeater, the last-mentioned means being controlledwhen the number of impulses transmitted from the repeater corresponds tothe digit registered in the one of the registers. Further the systemcomprises means controlled when a cycle of operation of the switchingmeans is completed for completing a cycle of operation of the impulsetransmitter.

In accordance with a further feature of the invention the systemcomprises an impulse generator, means for connecting the register to therepeater and for connecting the repeater to the impulse generator, meanscontrolled when the repeater is connected to the impulse generator forinitiating operation of the impulse transmitter, means controlled whenthe number of impulses in the series of register control impulsestransmitted from the impulse transmitter to the register corresponds tothe digit registered therein for disconnecting the register from therepeater, and means controlled when the register is disconnected fromthe repeater for arresting operation of the impulse transmitter and fordisconnecting the repeater from the impulse generator. Moreparticularly, the impulse generator is operative repeatedly through acycle to transmit a start impulse and then at least one control impulse;and the arrangement for controlling the repeater includes a controlnetwork operative to condition the impulse transmitter in response to astart impulse transmitted from the impulse generator and then to causeoperation of the impulse transmitter after it is conditioned in responseto control impulses transmitted from the impulse generator, thereby toprevent operation of the impulse transmitter to transmit a series ofswitch control impulses including a mutilated switch control impulse,and means for selectively operating the control network, thereby tocause the repeater to transmit a series of switch control impulsescomprising different numbers of switch control impulses.

In accordance with a further feature of the invention the systemcomprises a repeater network including a number of individual repeaterscommonly associated with the impulsing generator, a number of callingdevices, means for selectively connecting the calling devices to therepeaters, and means including the calling devices for selectivelycontrolling the operation of the repeaters from the impulse generator.More particularly, the repeater network is so connected and arrangedthat operation of the impulse generator is initiated when one of therepeaters is connected thereto, and operation of the impulse generatoris arrested when each of the repeaters is disconnected therefrom.

In accordance with a further feature of the invention the impulsegenerator comprises a control network including rst and second relays,first and second conductors, and means for impressing cyclically at apredetermined rate upon the first conductor and then upon the secondconductor a predetermined potential, the control network being soconnected and arranged that each odd time the potential is impressedupon the first conductor the first relay is operated, each o'dd time thepotential is impressed upon the second conductor the second relay isoperated, each even time the potential is impressed upon the firstconductor the rst relay is restored, and each even time the potential isimpressed upon the second conductor the second relay is restored,whereby the rst and second relays are controlled cyclically at one-halfthe predetermined rate. Also the impulse generator includes an impulsetransmitting network governed by the cyclical control of the first andsecond relays. Also the impulse generator includes a signal and meansgoverned by a predetermined departure by the first and second relaysfrom the cyclical control at one-half the predetermined rate forcontrolling the signal.

In accordance with a further feature of the invention the network in theimpulse generator comprises a timing relay, iirst and second condensers,a first series circuit for charging the first condenser and forenergizing the relay, a second series circuit for charging the secondcondenser and for energizing the relay, a first series path fordischarging the rst condenser and for energizing the relay, a secondseries path for discharging the second condenser and for energizing therelay, cyclically operating control means for completing the firstcircuit'and the second path and then for completing the second circuitand the rst path, thereby intermittently to energize the timing relay inorder to cause intermittent operation thereof, and means governed by theintermittent operation of the timing relay.

Further features of the invention pertain to the particular arrangementof the circuit elements thereof, whereby the above-outlined andadditional operating features are attained.

The novel features believed to be characteristic of the invention areset forth with particularity in the appended claims. rI"he invention,both as to its organization and method of operation, together withfurther objects and advantages thereof, will best be understood byreference to the following specification taken in connection with theaccompanying drawings in which Figure 1 illustrates the generalarrangement of a telephone system including a central exchange and adistant exchange and embodying the present invention; and Figs. 2 to 6,inclusive, taken together, illustrate the details of a system havingincorporated therein the features of the invention, as briefly outlinedabove,

DESCRIPTION or* rnc APPARATUS INCORPORATED 1N THE SYSTEM Referring nowmore particularly to Fig. lof the drawings, the telephone system 'thereillustratedoomprises a central exchange 2li, a distant' exchange 10, arst group of one-way trunk 'lines extending from 'the distant exchangefi to the central exchange 20, including the trunk line 50, and a secondgroup of one-way trunk lines extending from the centralexchange' 20 tothe distant exchange 1i), including the'trunkv line Sil. The centralexchange 2U is of the semi-automatic 'type serving a number of manualsubscriber substations, including the subscriber substations C and D; Atelephone line having a line circuit individually associated therewithextends to each 'subscriber substation'in the centralexchange 2t; thetelephone lines 'M and'112 having `the line circuits 45 'and 46respectively associated therewith extend to the subscriber substaions Cand D, respectively. The distant exchange lll is of the semi-automatictype serving a number of manual subscriber substations, includingthesubscribersubstations A` and B. A telephone linehaving a line circuitand anonnum'erical automatic Vswitch individually associated therewithextends to each subscriber substation' in the distant exchange' 10; thetelephone lines V'H and 'i2 having the line circuits 'i5 and "it and thenon-numerical automatic switches 18 `and T9 respectively associatedtherewith extend to the subscriber substations A and B, respectively.

Each trunk line in the first group' of` trunk lines extending from thedistant exchange 10 to Lthe central exchange20 terminates in a trunkcircuity in the distant exchange 'l0 and in aiselectorY repeater in thecentral exchange 20. For example, the'trunk line` 50 in the rst'group oftrunk lines4 terminates in the trunkA circuit 80 in the distant exchange10 and in the selector redistant exchange 'l0 terminates in a repeaterin thecentral exchange 2U and in an incoming selector switch in thedistant exchange 10. For example, the trunk line 60 in the second group'of trunk lines terminates in the repeater 65 in the central exchange2i] and inthe incoming selector switch in thek distant exchange 1i).Also the distant exchange 10 comprises a switch train'including, inaddition to the group of non-.

numerical automatic switches and the group of incoming selectorswitches, a number of groups of connector switches, one of the groups ofconnector switches including the vconnector switch 95. Eachnon-numerical automatic switch has access'to each of the trunk circuits;each of the incoming selector switches has access to the connectorswitchesin the various groups of connector switches; while the connectorswitches in the various groups of connector switches have access to thevarious groups of telephone lines.

Also the central exchange 20 comprises, in addition to the group ofselectorrepeaters and the groupy of repeaters, a local automatic switchtrain 2|, a switchboard provided with a number of operator positionsincluding the rst operator position 30, a main master impulse generator22, and an auxiliary master impulse generator 23. Preferably eachoperator position is identical to the rst operator position 3,0, whichcomprises operator telephone and control equipment 3|, operatorconnecting apparatus 32, and a key sender 33.

Each of the selector repeaters is accessible to each of the operatorpositions, thereby to allow the operator at any operator position toanswer a call from the distant exchange to the central exchange 20 onthe selector repeater. Furthermore, each selector repeater has access toeach repeater and to the local automatic switch train 2|. The localautomatic switch train 2| is accessible to each telephone line in thecentral exchange 20, and to each operator position, and has access toeach operator position, to each telephone line in the central exchange20 and to each of the repeaters. Finally, the main master impulsegenerator 22 and the auxiliary master impulse generator 23 are commonlyassociated with the repeaters and are operative to control the variousrepeaters and the key senders at the various operator positions, in amanner more fully explained hereinafter.

Each subscriber substation in the central exchange 20 and eachsubscriber substation in the distant exchange 10 is provided withsubstation equipment including a telephone instrument and a ringer. Theline circuits individually associated with the telephone lines in boththe central exchange 20 and the distant exchange 10 are of conventionalconnection and arrangement. Also the non-numerical automatic switches inthe distant exchange 10 are of a conventional type; while the incomingselector switches and the connector switches in the distant exchange 10are of the well-known Strowger type.l

Preferably, each of the trunk circuits in the distant exchange 10 isidentical to the trunk circuit 80 which comprises, as best shown in Fig.2, a number of relays including a line relay R220, a hold relay R230, abusy relay R240 and a bridge relay R250, connected and arranged in amanner more fully described subsequently.

Preferably, each of the selector repeaters in the central exchange 20 isidentical to the selector repeater 55 which comprises, as best shown inFig. 3, a switching mechanism 300 of the 100- point Strowger type,including a carriage provided with a wiper set including the wipers 30|,302, 303 and 304, the wipers mentioned being capable of both verticaland rotary movements. Further the mechanism 300 comprises acircumferentially disposed main contact bank associated with the wiperset, the wiper set having access to a group of one hundred linesterminated by the main contact bank. Also the mechanism 300 is providedwith a Vertical magnet M305 for moving the wiper set thereof in thevertial direction, a rotary magnet M301 for moving the wiper set thereofin the rotary direction, and a release magnet M309 for releasing thewiper set thereof and for causing the wiper set to lbe returned to itsnormal position. Finally the switching mechanism 300 has a number ofswitch springs S3|0, S3| I, S3|2, S3|3, S3|4, S3|5 and S3|8 operativelyassociated therewith, which are controlled in accordance with themovements of the wiper set thereof, in a manner more fully explainedsubsequently.

Also the selector repeater 55 comprises a number of relays including aline relay R325, two hold relays R330 and R360, a start relay R340, asend relay R345, an answer relay R350, an impulse relay R310, a controlrelay A315, a transfer relay R380 and a switching relay R390, connectedand arranged in a manner more fully described subsequently.

in the associated group of repeaters.

Preferably, each of the repeaters in the central exchange 20 isidentical to the repeater 65 which comprises, as best shown in Fig. 5, arepeater transformer 500 and a number of relays including a dial impulserelay R5I0, an answer relay R5l5, a control relay R520, a start relayR525, a revertive impulse relay R530, a digit relay R535, a pickup relayR540, a hold relay R550 and a timing relay R560, connected and arrangedin a manner more fully described subsequently.

The local automatic switch train 2| is of a well-known type, includingfinder switches, selector switches and connector switches, each being ofthe all-relay type, wherein the selector switches and the connectorswitches are operative to transmit revertive control impulses, in amanner more fully explained subsequently.

Preferably, each operator position in the central exchange 20 isconnected and arranged in a conventional manner, the operator telephoneand control equipment 3|, the operator connecting apparatus 32 and thekey sender 33 individually associated with the rst operator position 30being of well-known types. More particularly, the operator telephone andcontrol equipment 3| comprises a telephone instrument, not shown, and anumber of control keys, not shown, for setting up and supervisingconnections at the rst operator position 30; the key sender 33 comprisesa key set, not shown, and a number of registers including the firstregister 400; and the operator connecting apparatus 32 comprises anumber of connect keys, individually associated with the trunks in afirst group of trunks extending to the group of selector repeaters and asecond group of trunks extending to the local automatic switch train 2|,and a number of supervisory lamps. For example, the connect key K440 inthe operator connecting apparatus 32 is individually associated with thetrunk 35 extending to the selector repeater 55 and has individuallyassociated therewith a line lamp L441 and an answer lamp L44B; while theconnect key K445 is individually associated with the trunk 34 extendingto the local automatic switch train 2| and has individually associatedtherewith a line lamp and an answer lamp, not shown.

Preferably, both the main master impulse generator 22 and the auxiliarymaster impulse generator 23 in the central exchange 20 are identical andare commonly associated with each repeater As best shown in Fig. 6, themain master impulse generator 22 comprises two impulse relays R600 andR6|0, two cycle relays R620 and R630, a start relay R640, a timing relayR650, a lockout relay R350 and a hold relay R610, connected and arrangedin a manner more fully described subsequently. Also the main masterimpulse generator 22 comprises an interrupter 1680, two supervistorylamps L6I1 and LBIB and a reset key K516. The master impulse generators22 and 23 are so connected and arranged that the main master impulsegenerator 22 is normally operatively associated with the repeaters inthe associated group of repeaters and is adapted, in the event offailure thereof, operatively to associate the auxiliary master impulsegenerator 23 with the repeaters in the associated group of repeaters.

A better understanding of the connection and arrangement of thetelephone system will be facilitated from a consideration of the generaloperation of the various pieces of apparatus incorporated thereinincident to the completion and handling of Various calls at the firstoperator position 39 in the central exchange 20, as will appearhereinafter.

General operation of the system operator position in the centralexchange 2i! and then extended from the operator position to the varioussubscriber substations in both the central exchange and in the distantexchange lll. Y

For example, when a call is initiated at the subscriber substation C inthe central exchange 29, the line circuit 45 individually associatedwith the telephone line 4| is controlled, thereby to cause the localautomatic switch train 2| to opcrate and seize the telephone line 4| andan idle trunk, such as the trunk 34, extending to' the operatorpositions. When the trunk SLi-is thus seized, signals are transmitted tothe various operator positions in the central exchange 20; whereupon theoperator at one of the operator positions, such, for example, as theiirst operator position 30, answers the call by operating the connectkey KMS in the operator connecting apparatus 32 individually associatedwith the trunk 34 and is advised concerning the extension of the call.

In the event the call is to be extended to another subscriber substationin the central exchange 23, such, for example, as the subscribersubstation D, the operator at the rst operator position 39 thenregisters in the key sender 33 the appropriate digits in order tocontrol the operation of the local automatic switch train 2|. The localautomatic switch train 2| then operates to seize the telephone line 42extending to the subscriber substation D. The subsequent operation ofthe local automatic switch train 2| depends upon the idle or busycondition of the` subscriber substation D in accordance withconventional practice. The operator at the rst operator position 39 thenreturns the connect key K45 in the operator connecting apparatus 32 backto its normal position, thereby to release the apparatus at the firstoperator position 39.

On the other hand, in the event the call is to be extended to asubscriber substation in the distant exchange lil, such, for example, asthe subscriber substation B, the operator at the rst..

exchange 75 to extend the call to the subscriber ,y

substation B in the distant exchange I is explained more fullyhereinafter. After operation oi the repeater 55 and the previouslymentioned apparatus in the distant exchange 7|), the` operator at thefirst operator position 35 returns the f connect key KME in the operatorconnecting apparatus 32 back to its normal position, thereby to releasethe apparatus at the first operator position 30.

For example, when a call is initiated at the subscriber substation 'A inthe distant exchange 70, the-line circuit 15 individually associatedwith the'telephone line is controlled, thereby to cause thenon-numerical automatic switch 18 to seize an idle trunk in the group oftrunksextending to the associated trunk circuits, such, for example, asthe trunk 8| extending to the trunk circuit 80. When the trunk 8| isthus seized the trunk Vcircuit 80 operates, thereby to cause operationof the selector repeater by way of the associated trunk line 50,whereupon signals are transmitted to the various operator positions inthe central exchange 2|). The operator at one of the operator positions,such, for example, as the rst operator position 30, answers the call byoperating the connect key K440 in the operator connecting apparatus 32individually associated with the trunk 35 extending to the selectorrepeater 55 and is advised concerning the extension of the call. l

In the event thel call is to be extended to a subscriber substation `inthe central exchange 29, such, for example, as thesubscriber substationD, the yoperator at the first operator position 30 then'registers in thekey sender 33 the appropriate digits in order to control the operationofthe selector repeater 55 and the local automatic vswitch train 2 Thelocal automatic switch train2 |l then operates to seize thetelephoneline L12 extending to the subscriber substation D. The subsequentoperation of the local automatic switch train 2| depends upon the idleor busy condition of the subscriber substation D, as previously noted.The operator at the first operator position 3|! then returns the connectkey KMU in the operator connecting apparatus 32 back to its normalposition, thereby to release the apparatus at the first operatorposition 3U.

On the other hand, in the event the call `is to ybe Vextended to asubscriber substation in the distant exchange 10, such, for example, asthe subscriber substation B, the operator at the lirst operator position13.0'then registers in the key sender 33 the appropriate digits in orderto control Vthe operation of the, selector repeater 55, whereupon theselector repeater 55 operates to seize an idle .trunk'in the group oftrunks extendingy lto the group of repeaters, such, for examp1e,as thetrunk 31 extending to the Arepeater When the trunk 31 is thus seized therepeater operatesin orderto condition the incoming selector switch inthedistant exchange 10 by way of the associated trunk line-6|] and toinitiate operation of the main master impulse generator 22, in the eventit is not already operating. The main master impulse generator 22 causesimpulses corresponding to the impulses registered in the variousregisters in the key sender 33 to be transmitted by way of the repeater65 over the trunkline 6|) to the incoming selector switch 99, ytherebyto cause operation of the incoming selector switch 90 and the succeedingconnector switch. More particularly, the incoming selector switch 99 isoperative to select an idle one of the connector switches in-one of thegroups of connector switches, such, for example, as the connector switch95. The connector switch is -then operated to seize the telephone line12 extending to the subscriber substation B in the distant exchange l0.The subsequent operation of the connector switch 95 depends upon theidle or busy condition of the subscriber substation B vin accordancewith conventional practice.

After the repeater 65 is thus operated, the operator at the rst operatorposition 30 returns the connect key K440 in the operator connectingapparatus 32 back to its normal position, thereby to release theapparatus at the iirst operator position 30. Y

It is noted that the release of an established connection between twosubscriber substations in the central exchange 20, between twosubscriber substations in the distant exchange 'l0 and between asubscriber substation in the central exchange 20 and a subscribersubstation in the distant exchange is primarily under the control of thesubscriber at the calling subscriber substation and is effected when thesubscriber at the calling subscriber substation performs a releaseoperation thereat.

Further it is noted that, in the event a false call is initiated on atelephone line in the distant exchange '10, such as the telephone line1| extending to the subscriber substation A, the call is extended by wayof one of the trunk lines, such as the trunk line 50, and the associatedselector repeater 55 to one of the operator positions in the centralexchange 20 to be answered. For example, the false call may be answeredat the first operator position 30 in the manner previously explained.After the operator at the first operator position 30 determines that thecall is a false call she operates the key sender 33, thereby to causethe selector repeater 55 to be operated in accordance with a singledigit, in a manner more fully described hereinafter. When the selectorrepeater 55 is thus operated the line circuit 15 individually associatedwith the telephone line 1| is operated in order to lock the telephoneline 1| out of service. The telephone line 1| remains locked out ofservice until the fault thereon is removed.

As previously noted, the main master limpulse generator 22 is operativeto control each repeater in the associated group of repeaters and is soconnected and arranged that, in the event it fails properly to operate,it operates subsequently, thereby to intiate operation of the auxiliarymaster impulse generator 23, whereby the auxiliary master impulsegenerator 23 ls rendered operative to control each repeater in theassociated group of repeaters. Finally it is noted that both the mainmaster impulse generator 22 and the auxiliary master impulse generator23 are operative to control simultaneously a large number of repeatersin the associated group of repeaters, the repeaters in the associatedgroup being divided into odd and even subgroups.

Detailed operation of the system A call from a subscriber substation inthe distant exchange 10, such as the subscriber substation A, is rstinitiated by removing the receiver of the telephone instrument thereatfrom its associated switchhook, thereby to cause operation of the linecircuit individually associated with the telephone line 1| extending tothe subscriber substation A. Upon operating, the line circuit 'l5 marksthe telephone line 1| extending to the subscriber substation A as busyto the switches having access thereto and initiates operation of thenon-numerical automatic switch 18 individually associated with thetelephone line 7|, whereupon the non-numerical automatic switch 'I8operates to seize an idle trunk accessible thereto, such as the trunk 8|extending to the trunk circuit 80, the trunk 8| being marked as idle bythe absence of ground potential upon the control conductor C203 thereof.When the nonnurnerical automatic switch 18 seizes the trunk 8| a loopcircuit is completed between the subscriber substation A and the linerelay R220 in the trunk circuit 80, this circuit extending from groundby way of the lower winding of R 220 to the line conductor C202 of thetrunk 8| and from battery by way of the upper winding of R220 to theline conductor C20| of the trunk 8|, the line conductors C20| and C202of the trunk 8| being connected by Way of the non-numerical automaticswitch T8 and the telephone line 1| to the subscriber substation A. Whenthis loop circuit is completed the line relay R220 operates tointerrupt, at the contacts 223, a circuit traced hereinafter forenergizing the winding of the busy relay R240 to prepare, at thecontacts 22|, a circuit traced hereinafter for energizing the Winding ofthe bridge relay R250 and to cornplete, at the contacts 224, a path forapplying ground potential to the line conductor C2|| of the trunk line50 extending between the trunk circuit in the distant exchange 10 andthe selector repeater 55 in the central exchange 20. 'The path forapplying ground potential to the line conductor C2| of the trunk line 50extends from ground by way of the contacts 233 and. 224 to the lineconductor C2|| of the trunk line 50.

The application of ground potential to the line conductor C2|| of thetrunk line 50 completes a circuit for energizing the winding of thestart relay R340 in the selector repeater 55, this circuit extendingfrom the grounded line conductor C2|| of the trunk line 50 by way of theset of switch springs S3|0, the contacts 362 and the winding of R340 tobattery. When thus energized the start relay R340 operates to complete,at the contacts 34|, a path for applying battery potential by way of theupper winding of the line relay R325 to the line conductor C2 0 of thetrunk line 50, thereby to complete a circuit for energizing in seriesthe upper winding of the line relay R325 in the selector repeater 55 andthe winding of the bridge relay R250 in the trunk circuit 80. Thiscircuit extends from ground by way of the contacts 233 and the windingof R250 to the contacts 22| and from' ground by way of the resistor 242and the contacts 252 to the contacts 22| and from the contacts 22| byway of the line conductor C2|0 of the trunk line 50, the contacts 34|and 38| and the upper winding of R325 to battery. When thus energizedthe bridge relay R250 in the trunk circuit 80 and the line relay R325 inthe selector repeater 55 operate.

Upon operating, the bridge relay R250 interrupts, at the contacts 252,the previously traced multiple path in the above-traced circuit,including the resistor 242, and completes, at thev contacts 253, anobvious circuit for energizing the winding of the hold relay R230. Whenthus energized the hold relay R230 operates to complete, at the contacts234, an obvious path for applying ground potential to the controlconductor C203 of the trunk 8|, thereby to mark the trunk 0| in thetrunk circuit 80 as busy to the nonnumerical automatic switches havingaccess thereto. Further the hold relay R230 interrupts, at the contacts232, a further point in the previously mentioned circuit for energizingthe winding of the busy relay R240 and interrupts, at the contacts 233,the previously traced circuit for energizing in series the winding ofthe bridge relay R250 in the trunk circuit 80 and the upper winding ofthe line relay R325 in the selector repeater 55, a loop circuit tracedhereinafter M309 of the switching mechanism 300 and corn-v beingcompleted at this time, including the winding of the bridge relay R250inthe trunk circuit 80 and the upper and lower windings of the linerelay R325 in the selector repeater 55. Finally the hold relay R230completes, at the contacts 23|, a connection between the Iline conductorC202 of the trunk 8| and the line conductor C2|| of the trunk line 50.Accordingly, at this time, the line conductor C| of the trunk 8| isoperatively connected by way of the condenser 225 and the contacts tothe line conductor C2|6 of the trunk line while the line conductor C202of the trunk 8| is operatively connected by way of the condenser 226 andthe contacts 23| to the line conductor C2|| of the trunk line 53.

Upon operating, the line relay R325 in the selector repeater completes,at the contacts 326, the previously mentioned loop circuit forenergizing in series the winding of the b-ridge relay R253 in the trunkcircuit 80 and the upper and lower windings of the line relay R325 inthe selector repeater 55, this circuit extending from ground by way ofthe set of switch springs S3 |3, the contacts 353 and 325, the lowerwinding of R325, C2i l, the contacts 224, the Winding of R250, thecontacts 22|, C2l0, the contacts 34| and 38| and the upper winding ofR325 tc battery. Also the line relay R325 completes, at the contacts326, a series holding circuit for energizing the lower winding thereofand the winding ating, the hold relay R330 completes, at the contacts333, an alternative loop circuit for energizing in series the winding ofthe bridge relay R250 in the trunk circuit 80 and the upper and lowerwindings of the line relay R325 in the selector repeater 55; and analternative series circuit for energizing the lower winding of the linerelay R325 and the winding of the start relay R340, these circuitsextending from ground by way of the contacts 3|`| of the set of switchSprings S3l5, the contacts 333 and the lower winding of R325 to the lineconductor C2|| of the trunk line 50; and therefrom, by Way of thepreviously traced circuits to battery at the upper winding of the linerelay R325 and to battery at the winding of the start relay R340,

Also the hold relay R333 completes, at the contacts 332, a direct loopcircuit for energizing in series the winding of the bridge relay R250 inthe trunk circuit 80 and the upper and lower windings of the line relayR325 in the selector repeater 55, 'this circuit extending from ground byway of the set of switch springs S3|3 and the contacts 353 and 326 andfrom ground by way of the contacts 3|'l of the set of switch springsS3|5 and the contacts 333, by way of the lower winding of the line relayR325 to the line conductor C2|| of the trunk line 50, and therefrom byway of the previously traced path, including the winding of the bridgerelay R250 in the trunk circuit 30 to the line conductor C250 of thetrunk line 50, and 'therefrom by way of the contacts 332 and the upperwinding of R325 to battery. Further the hold relay R330 interrupts, atthe contacts 334, a point in a circuit traced hereinafter for energizingthe release magnet pletes, at the contacts 336, a circuit for energizingthe upper winding of the transfer relay R380, this circuit extendingfrom ground by way of the contacts 336, 342 and the upper winding ofR380 to battery. When thus energized the transfer relay R380 operates toprepare, at the contacts 384, a circuit traced hereinafter forenergizing the Vertical magnet M305 of the switching mechanism 300 andto prepare, at the contacts 385, a circuit traced hereinafter forenergizing the winding of the rotary magnet M301 of theV switchingmechanism 300.

Further, the hold relay R330 completes, at the contacts 336, a path forapplying ground potential to the control conductor C454 of the trunk 35extending between the selector repeater 55 and the operator connectingapparatus at the various operator positions, this path extending fromground by way of the contacts 336, 343 and 355 'to the control conductorC454 of the trunk 35. The application of ground potential to the controlconductor C454 of the trunk 35 completes obvious multiple circuits forilluminating the line lamps in the operator connecting apparatus at thevarious operator positions. For example, the line lamp L441 in theoperator connecting apparatus 32- at the first operator position 30 isilluminated, thereby to indicate to the operator thereat that there is acall from the distant eX- change 10 on the selector repeater 55 waitingto be answered. Assuming that the call is answered at the first operatorposition 30, this is accomplished by operating the connect key K440 inthe operator connecting apparatus 32 indi- Vidually associated with thetrunk 35. When the connect key K440 is thus operated there is completed,at the contacts 443 thereof, an obvious path for applying batterypotential by way of the cable 480 and the resistor 448 to the controlconductor C453 of the trunk 35 and obvious multiple circuits forilluminating the answer lamps L446, etc., in the operator connectingapparatus 32, etc.. The illumination of the answer lamp L446, etc., inthe operator connecting apparatus 32, etc., indicates to the operatorsat the various operator positions thatthe connect key in one operatorconnecting apparatus occupies its operated position, thereby to completea connection between the selector repeater 55 and the associatedoperator position.

The application of battery potential to the control conductor C453 ofthe trunk 35 completes a circuit for energizing the winding of theanswer relay R350, this circuit extending from ground by way of thecontacts 336, 343 and the winding of R350 to battery potential upon thecontrol conductor C453 of the trunk 35. When thus energized the answerrelay R350 operates to interrupt, at the contacts 355, the previouslytraced circuits for illuminating the line lamps, L441, etc., in theoperator connecting apparatus 32, etc., thereby to indicate to theoperator at the first operator position 30 that the selector repeater 55has been conditioned to be responsive to operation of the key sender 33,in a manner more fully explained hereinafter. Also when the connect keyR440 in the operator connecting apparatus 32 is thus operated there iscompleted, at the contacts 44| and 442 thereof, an obvious connectionbetween the line conductors C45! and C452 of the trunk 35 and the trunkconductors C43| and C432 at the rst operator position 30, both theoperator telephone and control equipment 3| and the key sender 33 beingdirectly Also, upon operating, the answer relay R350 completes, at thecontacts 354, a circuit for energizing the winding of the hold relayR360, this circuit extending from ground by way of 'the set of switchsprings S3I3, the contacts 354 and the winding of R360 to battery. Whenthus energized the hold relay R360 operates to interrupt, at thecontacts 362, the previously traced holding circuit for energizing inseries the lower winding of the line relay R325 and the winding of thestart relay R340 and to complete, at the contacts 363, an alternativeholding circuit for energizing the winding of the start relay R340. Thelast-mentioned circuit extends from ground by way of the contacts 336,342 and 363 and the winding of R340 to battery. Accordingly, the startrelay R340 remains in its operated position. Also the line relay R325remains in its operated position due to the completed direct loopcircuit including the winding of the bridge relay R250 in the trunkcircuit 80 and the upper and lower windings of the line relay R325 inthe selector repeater 55. Also the hold relay R360 prepares, at thecontacts 36|, a circuit traced hereinafter for energizing the lowerwinding of the control relay R315 and prepares, at the contacts 364, acircuit traced hereinafter for energizing the winding of the impulserelay R310. Finally the answer relay R350 completes, at the contacts352, an operative connection between the operator telephone and controlequipment 3| at the first operator position 30 and the trunk line 50,this connection extending from the line conductor C2|0 of the trunk line50 by way of the condenser 32|, the contacts 346, the line conductorC45| of the trunk 35, the contacts 44| of the connect key K440 and thetrunk conductor C43| to the operator telephone and control equipment 3|;and from the line conductor C2! I of the trunk line 50 by way of thecondenser 322, the contacts 352, the line conductor C452 of the trunk35, the contacts 442 of the connect key K440 and the trunk conductorC432 to the operator telephone and control equipment 3|. As previouslynoted, the telephone instrument at the subscriber substation A isoperatively connected by way of the telephone line 1|, the non-numericalautomatic switch 10, the trunk 8| and the trunk circuit 80 to the trunkline 50 at this time; while the trunk line 50 is operatively connectedby way of the selector repeater 55, the trunk 35 and the connect keyK440 to the operator telephone and control equipment 3| at this time.Accordingly, the telephone instrument at the subscriber substation A inthe distant exchange 10 is operatively connected to the operatortelephone and control equipment 3| at the rst operator position 30 inthe central exchange 20, whereupon the subscriber at the subscribersubstation A and the operator at the rst operator position 30communicate with each other, the operator at the first operator position30 being advised concerning the extension of the call.

After answering the call on the trunk line 50, the operator at the firstoperator position 30 may extend the call to any subscriber substation inthe central exchange 20 or to any subscriber substation in the distantexchange 10. Assuming that the call is to be extended to a subscribersubstation in the central exchange 20, such as the subscriber substationD, the operator at the first operator position 30 initiates theextension of the call by operating the key sender 33, therebridgedacross the trunk conductors C43I and by to cause a number of digits tobe registered in the several registers included therein andcorresponding to the switch train route, including the selector repeater55 and the local automatic switch train 2|, to the telephone line 42extending to the subscriber substation D. More particularly, the rstdigit is registered in the first register 400 in the key sender 33;whereupon the register switch S4|0 therein is operated away from itsnormal position and the digit switch S420 therein is set such that it isoperated away from its normal position when a predetermined number ofimpulses corresponding to the digit registered in the first register 400have been transmitted over the trunk 35 to the selector repeater 55.Similarly, the second, third, etc., digits are registered in the second,third, etc., registers in the key sender 33. When the register switchS4|0 in the iirst register 400 in the key sender 33 is operated awayfrom its normal position, there is completed a path for applying groundpotential in the rst register 400 t0 the line conductor C452 of thetrunk 35, this path extending from ground by Way of the contacts 424 ofthe digit switch S420 in the first register 400, the contacts 4|2 of theregister switch S4|0 in the first register 400, the trunk conductor C432and the contacts 442 of the connect key K440 to the line conductor C452of the trunk 35. This application of ground potential to the lineconductor C452 of the trunk 35 completes an obvious circuit forenergizing the winding of the send relay R345 in the selector repeater55, thereby to cause operation of the send relay R345. Upon operating,the send relay R345 completes, at the contacts 348, an obvious holdingcircuit for eriergizing the winding of the answer relay R350 andcompletes, at the contacts 341, the previously mentioned circuit forenergizing the lower winding of the control relay R315. The circuit forenergizing the lower winding of the control relay R315 extends fromground by way of the contacts 341, 36|, 31| and 308 and the lowerwinding of R315 to battery. When thus energized the control relay R315operates to complete, at the contacts 316, a holding circuit forenergizing the lower winding thereof, this circuit extending from groundby way of the contacts 341, 316 and 308 and the lower winding of R315 tobattery. Further the control relay R315 completes, at the contacts 311,a circuit for energizing in series the winding of the impulse relay R310in the selector repeater 55 and the register magnet M425 in the iirstregister 400 in the key sender 33, this circuit extending from ground byway of the contacts 311 and 364, the winding of R310, the contacts 33|,the line conductor C45| of the trunk 35, the contacts 44| of the connectkey X440, the trunk conductor C43l, the contacts 4| of the registerswitch S4I0 in the first register 400, the contacts 42| of the digitswitch S420 in the first register 400 and the winding of M425 tobattery. When this circuit is completed the impulse relay R310 and theregister magnet M425 operate.

Upon operating, the register magnet M425 in the first register 400operates the associated pawl 426, thereby to condition the associatedratchet wheel 421 to be driven one step in the clockwise direction. Uponoperating, the impulse relay R310 completes, at the contacts 313, anobvious holding circuit for energizing the winding of the hold relayR360 and completes, at the contacts 312, a circuit for energizing theVertical magnet M305, this circuit extending from ground by Way of thecontacts 341, 316, 312 and 384 and the' vertical magnet M305 to battery.When thus energized the vertical magnet M305 operates to drive the wiperset of the switching mechanism 300- one step in the vertical directionand to complete, at the contacts 306,- a circuit for energizing theupper winding ofthe -control relay R315, this circuit extending fromground by way of the contacts 341, 316 and 306 and the upper winding ofR315 to battery. When both the upper winding and the lower winding ofthe control relay R315 are thus energized this relay restores, thecontrol relay R315 being of the differential type. Upon restoring, thecontrol relay R315 interrupts, at the contacts 311, the previouslytraced series circuit for energizing the winding of the impulse relayR310 in the selector repeater 55 and the register magnet M425 in the rstregister 400, thereby to cause the impulse relay R310 and the registermagnet M425 to restore.

Upon restoring, the register magnet M425 in the rst register 400releases the associated pawl 426, thereby to cause the pawl 426 to drivethe associated ratchety wheel 421 one step in the clockwise direction,thereby to effect registration of one impulse in the rst register 400.Upon restoring the impulse relay R310 interrupts, atr the contacts 312,the previously traced circuit.` for energizing the vertical magnet M305,u

thereby to cause the vertical magnet to restore. Upon restoring, thevertical` magnet M305 interrupts, at the contacts 306, the -previouslytraced circuit for energizing the upper winding of the -control relayR315. the control relay R315 interrupts, at the contacts 316, thepreviously traced holding circuit for energizing the lower windingthereof. Finally, upon restoring, the impulse relay R310 recompletes, atthe contacts 31|, the previously traced original circuit for energizingthe lower winding ofthe control relay R315.

Accordingly, the control relay R315 reoperates, thereby to recomplete,at the contacts 311, the previously traced series circuit for energizingthe winding of the impulse relay R310 in the selector repeater 55 andthe register magnet M425-in the iirst register 400 in the key sender 33,whereupon the impulse relay R310 and the register magnet M425 reoperate.Upon reoperating, the control relay R315 recompletes, at the contacts316, the previously traced holding circuit for. energizing the lowerwinding thereof; and upon operating, the impulse relay R310reco-mpletes, at the contacts 312, the previously tracedcircuit forenergizing the vertical magnet M305, thereby to cause the verticalmagnet M305 to reoperate. Upon reoperating, the vertical magnet M305recompletes, at the contacts 306,` the previously traced circuit forenergizing the upper winding of the control relay R315, thereby to causethe latter relay to restore.

Accordingly, the impulse relay R310, the control relay R315 and thevertical magnet M305 interact in the above-described manner, thereby tocause the vertical magnet M305 to drive the wiper set of the switchingmechanism 300 step by step in the vertical direction and to cause theregister magnet M425 to drive the associated ratchet wheel 421 step bystep in the clockwise direction. When the wiper set of the switchingmechanism 300 has been driven in the vertical direction a number ofsteps corresponding to the impulses of the digit registered in the rstregister 400 in the key sender 33, the ratchet Also, upon restoring,

wheel, 421 is drivenk a corresponding number. of steps in the clockwisedirection, thereby to cause thel digit switch S420 inthe liirst register400 to be operated away from -its normal position. When the digit switchS420 in the rstl register 400 is operated away from its normal positionthere is. completed, at the contacts 423 thereof, a path substantiallyidentical to that previously traced for applying ground potential in thesecond register by way of the control conductor C416 extending theretovto the line conductor C452 of the trunk 35, thereby to retain completedthe previously mentioned circuity for energizing the winding of the-send relay R345 in the selector repeater 55. 424 of the register switchS420 in the rst reg'- ister 400, there is interruptedA the previouslytraced path for applying ground potential in the rst register 400 to theline conductor C452 of the trunk 35. Accordingly, the send relay R345 inthe selector repeater 55 remains in its op'erated position at this time;Further, at the contacts 42| ofthe register switch S420 in the rstregister` 400, there is interrupted the previously traced path forapplying battery potential by way of the register magnet M425 in the rstregister 400 to the line conductor C45! of the trunk 35; and there isprepared, at the contacts 422 of the register switch S420 in the firstregister 400,

a path substantially identical to that previously traced for applyingbattery potential by way of Vthe register magnet in the second registerin the key sender 33 and the control conductor C415 extending thereto tothe line conductorv C45! of the trunk 35. At this point it is noted thatthere is a delay in the application oiv battery potential by way of theregister magnet in the second register in the key sender 33A to thevcontrol. conductor C415 and consequently to the line conductor C45! ofthe trunk 35. Accordingly, when the control relay R315 reoperates in'-cident to the restoration of the impulse' relay R310 and the verticalmagnet M305, the impulse relay R310 doesV not immediately operate as thepreviously mentioned circuit for energizing in series the winding of theimpulse relay R310 and the register magnet in the second register in thekey sender 33- is not immediately completed. This delay is produced inthe second register in the key sender 33 in order to allow the switchingmechanism 300- in the selector repeater 55 adequate time to operateautomatically and seize an idle trunk inthe previously selected group oftrunks, in a manner more fully explained subsequently.

At this point it is notedv that, when the wiper set-of the switchingmechanism 300 is driven one stepk in the vertical direction, the sets ofswitch springs S310 and S313 are actuated into disengagement and thesets of switch springs S3I I and S3I2 are actuated into engagement.Whenv the set of switch springs S3ll is actuated into engagement, a pathtraced hereinafter is prepared for applying ground potential to the lineconduce tor C2401v ofthe trunk line 50; and when the set of switchsprings S312 is actuated into engagement, a further point in thepreviously mentioned circuit for energizing the release magnet M309 isprepared. When the set of switch springs S310 is actuated intodisengagement, a further point in the previously traced original circuitfor energizing the winding of the start relay R340- is interrupted, thestart relay R340 being retained inA itsv operated position at this timekdue to thelcompleted holding circuit for en- Also, at the cont-actslergizing the winding thereof under the control of the operated holdrelay R360. When the set of switch springs S3I3 is actuated intodisengagement the previously traced original circuit for energizing `thewinding of the hold relay R360 is interrupted, the hold relay R360 beingretained in its operated position at this time due to the intermittentcompletion of the previously traced holding circuit for energizing thewinding thereof Iunder the control of the impulse relay R310, the

hold relay R360 being of the slow-to-release type. Accordingly, thestart relay R340 remains in its operated position, while the hold relayR360 remains in its operated position as long as the impulse relay R310is intermittently operated. However, after the digit switch S420 in thefirst register 400 in the key sender 33 is operated as previouslyexplained, battery potential is not immediately connected in the secondregister in the key sender 33 to the line conductor C45I of the trunk35. Accordingly, the impulse relay R310 remains in its restored positionfollowing the complete operation of the wiper set of the switchingmechanism 300 in the vertical direction.

Hence, shortly after the impulse relay R310 restores to interrupt, atthe contacts 313, the previously mentioned holding circuit forenergizing the winding of the hold relay R360, the latter relayrestores. Upon restoring, the hold relay R360 interrupts, at thecontacts 363, the previously traced holding circuit for energizing thewinding of the start relay R340, thereby to cause the latter relay torestore shortly thereafter, the start relay R340 being of theslow-to-release type.

Upon restoring, the start relay R340 interrupts,

at the contacts 34|, the original loop circuit for `energizing in seriesthe winding of the bridge relay R250 in the trunk circuit 80 and theupper and lower windings of the line relay R325 in the selector repeater55; however, the last-mentioned relays do not restore at this time dueto the previously traced completed alternative loop circuit forenergizing the windings thereof. Further the start relay R340interrupts, at the contacts 342, a further point in the previouslytraced holding circuit for energizing the winding thereof andinterrupts, at the contacts 342, the previously traced circuit forenergizing the upper winding of the transfer relay R380. However, thetransfer relay R300 does not immediately restore, this relay being ofthe slow-to-release type. Also the start relay R340 interrupts, at thecontacts 343, the previously traced original circuit for energizing thewinding of the answer relay R350, the latter relay remaining in itsoperated position at this time due to the completed holding circuit forenergizing the winding thereof. Finally, the start relay R340 prepares,at the contacts 344, a test circuit traced hereinafter for energizingthe winding of the switching relay R390.

Also, upon restoring, the hold relay R360 interrupts, at the contacts364, a further point in the previously traced circuit for energizing thewinding of the impulse relay R310 and completes, at the contacts 365, aholding circuit for energizing the lower winding of the transfer relayR380 and a circuit for energizing the rotary magnet M301, the controlrelay R315 occupying its operated position at this time. These circuitsextend from ground by way of the contacts 311 and 365 to the contacts385 and from the contacts 385 by way of the lower winding of R380 tobattery, and from the contacts 385 by way of the rotary magnet M301 tobattery. When the lower winding of the transfer relay R380 is thusenergized this relay remains in its operated position; and when therotary magnet M301 is thus energized it operates to drive the wiper setof the switching mechanism 300 one step in the rotary direction and tointerrupt, at the contacts 308, the previously traced circuit forenergizing the lower winding of the control relay R315, thereby to causethe latter relay to restore. Upon restoring, the control relay R315interrupts, at the contacts 311, the previously traced holding circuitfor energizing the lower winding of the transfer relay R380 and thepreviously traced circuit for energizing the rotary magnet M301. Whenthese circuits are interrupted the transfer relay R380 remains in itsoperated position, this relay being of the slow-to-release type; whilethe rotary magnet M301 restores to recomplete, at the contacts 308, atest connection between the control wiper 303 of the wiper set of theswitching mechanism 30D and the lower winding of the control relay R315.

At this time, the wiper set of the switching mechanism 300 engages thecontact set in the associated contact bank terminating the rst trunk inthe associated group of trunks extending to the local automatic switchtrain 2l. In the event the first trunk mentioned is busy, groundpotential appears upon the control conductor thereof, thereby tocomplete a circuit for energizing the lower winding of the control relayR315 and a path for short-circuiting the winding of the switching relayR390. The circuit for energizing the lower winding of the control relayR315 extends from the grounded control conductor of the trunk mentionedby way of the control wiper 303, the contacts 394, 382 and 308 and thelower winding of R315 to battery; while the path for short-circuitingthe winding of the switching relay R390 extends from the groundedcontrol wiper 303 by way of the contacts 394 and 362, the Winding ofR390, the contacts 3I9 of the set of switch springs S3|8, the contacts344 and 336 to ground. Accordingly, in the event the trunk mentioned isbusy, the control relay R315 reoperates while the switching relay R390remains in its restored position. Upon reoperating, the control relayR315 recompletes, at the contacts 311, the previously traced holdingcircuit for energizing the lower winding of the transfer relay R380 andthe previously traced circuit for energizing the rotary magnet M301,thereby to retain the transfer relay R380 in its operated position andto cause reoperation of the rotary magnet M301. Accordingly, the controlrelay R315 and the rotary magnet M301 interact in the manner describedabove, thereby to cause the wiper set of the switching mechanism 300 tobe driven step by step in the rotary direction until it selects an idletrunk in the group of trunks extending to the local automatic switchtrain2l.

When an idle trunk in the group of trunks extending to the localautomatic switch train 2i is thus selected, further operation of therotary magnet M301 is arrested due to the absence of ground potentialupon the control conductor thereof. More particularly, when no groundpotential is applied to the control wiper 303 the previously tracedcircuit for energizing the lower winding of the control relay R315 isnot recompleted and the previously traced path for shortcircuiting thewinding of the switching relay R390 is interrupted. Hence, at this time,a circuit is completed for energizing in series the lower winding of thecontrol relay R315 and the 'winding of the switching relay R390, thiscircuit extending from ground by way of the contacts 336 fand 344, thecontacts 3|9 of the set of switch springs 1S3|8, the windings of R390,thecontacts y308 and the lower winding of R315 to battery. When thisseries circuit is completed the switchingrelay R300 operates; however,the control relay-R315 does not reoperate due to the high seriesresistance Yof this circuit. Upon operating, the lswitching relay R390completes, at the contacts 395 and 396, obvious paths for applyingground potential to lthe control wipers 303 `and 304, respectively,thereby to cause ground potential to be applied to theY two controlconductors of the selected trunk in the group of trunks extending to thelocal switch train 2|, such as the trunk 36. Also, upon operating, theswitching relay R390 interrupts, vat the contacts 39|, a furtherY pointin the previously traced circuit for energizing the winding of theimpulse relay R310, 'and prepares, at the contacts 392 and 393,operative connections between the line conductors C2|0 and C2|| of thetrunk line 50 and the line conductors C41| and C412, respectively, ofthe trunk 39. Finally, the switching relay R390 completes,l at thecontacts 392, an operative connection between the line conductors C41|of the trunk 36 extending to the local automatic switch train 2| and theline conductor C45| of the trunk 35 extending to the key sender 33, fora purpose more lfully explained hereinafter. Shortly following theoperation of the control relay R315 the transfer relay R380 restores,thereby to interrupt, at the contacts 385, a further point in thepreviously tracedholding circuit for energizing the lower winding of thetransfer relay R380 and a vfurther point in the previously tracedcircuit for energizing the rotary magnet M301.

Accordingly, at this time, the selector repeater 55 has operated inresponse to the rst digit registered in the rst register 400 in the keysender 33 to select a group of trunks extending to the localautomaticswitch train 2| and has then operated automatically to select the idletrunk 36 in the .previously mentioned group of trunks extending to thelocal automatic switch train 2 When ground potential is applied to thecontrol conductors C413 and C414 of the trunk 36, the local automaticswitch train 2| is rendered responsive to additional digits registeredin the additional registers in the key sender 33 to operatesubsequently. Shortly following the complete operation of the selectorrepeater 55 the second register in the key sender 33 operates, therebyto cause battery potential to be applied by way of the register magnettherein to the control conductor C415 extending thereto and,accordingly, by way of the previously traced circuit to the lineconductor C45| of the trunk 35. The application of battery potential tothe line conductor C45| of the trunk 35 completes an obvious path,including the line wiper 30| of the wiper set of the switching mechanism300, for applying battery potential to the line conductor C41| oftheft'runk 36 extending to the local automatic switch train 2|. Thisapplication of battery potential to the line conductor. C41| of thetrunk 36 initiates operation of the local automatic switch train 2|whereupon the local automatic switch train 2| responds to the digitregistered in the second register in the key sender 33and causesrevertive impulses to be returned to the second'register in the keysender 33, thereby to control the transfer-of the circuit from thesecond register tolthe third register in thekey trunk 35.

sender 33, in a manner similar to the transfer of the connection fromthe iirst register 400 to the second register in the key sender.33,previously explained. Accordingly, the local automatic switch train 2|operates in accordance with the second, third, etc., digits registeredin the second, third,-etc., registers in the key sender 33, thereby toSeize the telephone line 42 extending to the subscriber substation D.The subsequent operation of the local automatic switch train 2| dependsupon the idle or busy condition of the telephone line 42, in a mannermore fully explained hereinafter.

After all of the digits registered in the various registers in the keysender 33 have been transmitted by way of the trunk 35, the selectorrepeater 55 and the trunk 36 to the local automatic switch train 2| inorder to cause operation thereof to seize the telephone line 42extending to the subscriber substation D in the manner previouslyexplained, the last register in the key sender 33 operates, thereby tocause ground and battery potential to be removed from the lineconductors C452 and 045|, respectively, of the When battery potential is`removed. from the line conductor 045| of the trunk 35, furtheroperation of the local automatic switch train 2| is arrested; and whenground potential is removed from the line conductor C452 of the trunk 35the previously traced circuit for energizing the winding `of the sendrelay R345 is interrupted, thereby to cause the latter relay to restore.Upon restoring, the send relay vR345 completes, at the contacts 346, aconnection traced hereinafter between the 'line conductor C2|0 of thetrunk line 50 and the line `conductor C41| of the trunk 36, andinterrupts, at the contacts 348, the previously traced holding circuitfor energizing the winding of the answer relay R350, thereby to causethe latter relay to restore and complete, at the contacts 35|,a-connection between the line conductor C2|| of the trunk line 50 andthe line conductor C412 of the trunk 36. At this time, the lineconductor C2|0 of the trunk line 50 is connected by way of the condenser32|, the contacts 346 and 392 and the line wiper 30| to the lineconductor C41| of the trunk 36,' and the line conductor C2|| of thetrunk line 50 is connected by way of the condenser 322, the contacts 35|and 393 and the line wiper 302 to the line conductor C412 of the trunk36; the trunk line 50 lbeing connected by way of the trunk circuit 80,the trunk 8|, the non-numerical automatic switch 18 and the telephoneline 1| to the subscriber sub-station A in the distant exchange 10 andthe trunk 36 being connected to the local automatic Switch train 2|.Also, when the previously tracedholding circuit for energizing thewinding of the answer relay R350 is interrupted, at the contacts 343,due to the restoration of the send relay R345, the re-v sistor 446included in the previously traced circuit for illuminating the answerlamp L446 in the operator connecting apparatus 32 at the first operatorposition 30 is unloaded somewhat, thereby to cause the answer lamp D446to be illuminated more brightly. When the answer lamp L446 is thusilluminated more brightly, it indicates to the operator at the firstoperator position 30 that the key sender 33 has been released. Theoperator at the operator position 30 then returns the connect key K440in the operating .connecting apparatus 32 to its normal position,thereby to interrupt, at the contacts 44| and442 thereof, the connectionbetween -both the operator ltelephone and control equipment 3| and thekey sender 33 and the trunk 35 extending to the selector repeater 55 andto render the first operator position 30 again idle. Also when theconnect key K440 is returned to its normal position there isinterrupted, at the contacts 443 thereof, the previously traced multiplecircuits for illuminating the answer lamps L446, etc., included in theoperator connecting apparatus 32, etc., at the various operatorpositions, thereby to indicate to the operator at the rst operatorposition 30 that the apparatus thereat is idle and available for use inanswering another call. f

In the event the called subscriber substation D in the central exchange20 is busy at this time, the local automatic switch train 2| operates toreturn busy tone current over the previously traced connection to thesubscriber substation A in the distant exchange 10, thereby to indicateto the subscriber thereat that the connection cannot be immediatelycompleted due to the busy condition of the called subscriber substationD. One the other hand, in the event the called subscriber substation Dis idle at this time, the local automatic switch train 2| operates tocause ringing current to be projected over the telephone line 42 to thecalled subscriber substation D and to cause ring-back tone current to bereturned over the previously traced connection to the calling subscribersubstation A, thereby to indicate to the subscriber at the subscribersubstation A that the called subscriber substation D in the centralexchange 20 is being rung. Also when the local automatic switch train 2|seizes the telephone line 42 extending to the called subscribersubstation D, the line circuit 46 individually associated therewithoperates, thereby to mark the telephone line 42 as busy to the switchesin the local automatic switch train 2| having access thereto. When thesubscriber at the called subscriber substation D answers the call thelocal automatic switch train 2| switches through, thereby to complete aconnection between the trunk 36 and the telephone line 42, in order tocomplete an established connection between the calling subscribersubstation A in the distant exchange and the called subscribersubstation D in the central exchange 20.

In the foregoing explanation of the mode of operation of the selectorrepeater 55 it was assumed that there was an idle trunk in thepreviously selected group of trunks extending to the local automaticswitch train 2| and that the selector repeater 55 seized the idle trunkin this group of trunks incident to the operation of the switchingmechanism 300 thereof in the rotary direction. However, it may occurthat there are no idle trunks in the previously selected group of idletrunks extending to the local automatic switch train 2|; in which eventthe control relay R315 and the rotary magnet M301 continue to operate inthe manner previously explained, in order to drive the wiper set of themechanism 300 step by step in the rotary direction until the wiper setis driven eleven steps away from its normal position. When the wiper setof the switching mechanism 300 is driven eleven steps away from itsnormal position the sets of switch springs S3| 5 and S3|8 are operated.More particularly, the contacts 3|9 of the set of switch springs S3 I8vare actuated into disengagement; while the contacts 320 of the set ofswitch springs S3|8 are actuated into engagement, thereby to complete analternative holding circuit for energizing the winding of the hold relayR360. This circuit extends from ground by way of the contacts 336 and344, the contacts 320 of the set of switch springs S318 and the windingof R360 to battery. When thus energized the hold relay R360 operates andcompletes, at the contacts 36|, the previously traced circuit forenergizing the lower winding of the control relay R315, thereby to causethe latter relay to operate. Upon operating, the control relay R315completes, at the contacts 311, the previously traced series circuit forenergizing the winding of the impulse relay R310 in the selectorrepeater 55 and the winding of the register magnet in the secondregister in the key sender 33, thereby to cause the impulse relay R310and the register magnet mentioned to operate. Also upon operating, thecontrol relay R315 completes, at the contacts 316, the previously tracedholding circuit for energizing the lower winding thereof. Uponoperating,the impulse relay R310 completes, at the contacts 312, analternative circuit for energizing the upper winding of the controlrelay R315, this circuit extending from ground by way of the contacts341, 316, 312 and 383 and the upper winding of R315 to battery. Whenboth the upper winding and the lower winding of the control relay R315are thus energized, this relay restores as it is of the differentialtype, as previously noted. Upon restoring, the control relay R315interrupts, at the contacts 316, the previously traced holding circuitfor energizing the lower winding thereof and interrupts, at the contacts311, the previously traced 'circuit for energizing the winding of theimpulse relay R310, thereby to cause the latter relay to restore. Uponrestoring, the impulse relay R310 interrupts, at the contacts 312, thepreviously traced alternative circuit for energizing the upper windingof the control relay R315 and recompletes, at the contacts 31|, thepreviously traced original circuit for energizing the lower winding ofthe control relay R315. Accordingly, the impulse relay R316 and thecontrol relay R315 interact in the above-described manner in order tocause all the digits registered in the second, third, etc., registers inthe key sender 33 to be transmitted, whereby the registers mentioned inthe key sender 33 are completely cleared, in the manner previouslydescribed, the same as though the selector repeater 55 had switchedthrough to seize the local automatic switch train 2| in the mannerpreviously explained.

When the set of switch springs S3| 5 is thus actuated the previouslytraced alternative loop circuit, including the winding of the bridgerelay R250 in the trunk circuit and the upper and lower windings of theline relay R325 in the selector repeater 55, is interrupted at thecontacts 3|1 thereof; and, at the contacts 3|6 of the set of switchsprings S3I5, there is completed a further loop circuit including thewinding of the bridge relay R250 in the trunk circuit 80 and the upperand lower windings of the line relay R325 in the selector repeater 55.This further loop circuit extends from ground by way of the winding of abusy tone transformer, not shown, the set of switch springs S3|4, theconta/cts 3|6 of the set of switch springs S3l5, the contacts 333, thelower winding of R325, C2||, the contacts 224, the winding of R250, thecontacts 22|, C2|0, the contacts 332 and the upper winding of R325 tobattery. Accordingly, busy tone current traverses the previously tracedfurther loop circuit, thereby to cause busy tone current to be projectedfrom the trunk circuit 80 over the trunk 8|, the

non-numerical automatic switch 18 and the telephone line 1l to thesubscriber substation A in the distant exchange in order tov cause thereceivery of the telephone instrument at the subscriber substation A toproduce busy tone. The subscriber at the calling subscriber substation Athen effects the release of the selector repeater 55 by replacing thereceiver of the telephone instrument at the subscriber substation A uponits associated switchhook.

-At this point it is noted that the release of the selector repeater 55,in the event it fails to nd an idle trunk in the previously selectedgroup ofv trunks extending to the local automatic switch train 2|, inthe manner described above, and the release of the establishedconnection between the calling subscriber substation A in the distantexchange 10 and the called subscriber substation D in the `centralexchange 20 are performed in an, identical manner under the control ofthe subscriber at the calling subscriber substation A. Moreparticularly, when the subscriber at the calling subscriber substation Ain the distant exchange 10 replaces the receiver of the telephoneinstrument thereat upon its associated switchhook the loop circuitbetween the line relay R220 in the trunk circuit 80 and the subscribersubstation A is interrupted, thereby to cause the latter relay torestore; also the line circuit individually associated with thetelephone line 1I extending to the subscriber substation A iscontrolled, thereby to initiate operation of the non-numerical automaticswitch 18 individually associated with the telephone line 1| extendingto the subscriber substation A. More particu- 9 larly, the non-numericalautomatic switch 18 is voperated to its normal position, whereupon theAline circuit 15 is controlled, thereby to mark the telephone line 1|extending to the subscriber substation A as idle to the switches havingaccess thereto.

Upon restoring, the line relay R220 interrupts, at the contacts 224, thepreviously traced series loop circuit, including the winding of thebridge relays R250 in the trunk circuit 80, and the upper and lowerwindings of the line relay R325 in the selector repeater 55, thereby tocause the latter relays torestore. Upon restoring, the bridge relay R250interrupts, at the' contacts 253,

the previously mentioned circuit for energizing H the winding of theholdrelay R230, thereby to cause the latter relay to restore shortlythereafter, the hold'relay R230 being of the slow-torelease type.Upon'restoring, the hold relay R233 interrupts, at the `contacts 234,the previously mentioned path for applying ground potential to thecontrol conductor C203 of the trunk 3l, thereby to mark the trunk 3| andthe trunk circuit 80 as idle to the non-numerical automatic switches'having access thereto. Upon restoring, `the line relay R325 interrupts,at the contacts 321, `the previously mentioned circuit forenergizin'gthe winding of the hold relay R330, thereby to .cause thelatter relay to restore shortly thereafter, the hold relay R330 being ofthe slow-torelease type. Upon restoring, the hold relay R330 completes,at the contacts 333, the previously mentioned circuit for energizing therelease magnet M333, this circuit extending from ground by way of thecontacts 334, the set of switch springs SM2 and the release magnet M339to battery. When thus lenergized the release magnet M339 operates,thereby to release the `'wiperset of the switching mechanism 300 inv(ill order to cause this wiper set to be .returned to its normalposition. When the-Wiper set of the switching mechanism 300 is returnedto its normal position, the sets of switch springs S310 and S313 areactuated into engagement; the sets-of switch springs S3!! andS3l2areactuated into disengagement; while thesets of switch springs S3l5 andS3I8 are actuated only in theevent they have been previously actuateddue to the failure of the selector repeater 55 to seize an idle'v trunkin the previously-selected group of trunks extending to the localautomatic switchtrain 2 I.

Assuming that the present release is eected incident to .the failure ofthe selector repeater 55 to seize a trunkin the previously selectedgroup of trunks extending to the local automatic switch train 2l, thecontacts 3|6 and 3I1 of the setof switch springs S3 l 5 are respectivelyactuated into disengagement and intoengagement; while the contacts 3|9and i320 of the set of switch springs S3 f8 are actuated 'respectivelyinto engagement and disengagement.Y Also upon restoring, the hold relayR330 interrupts, vat the contacts 333, a further point in the previouslytraced path for projectingbusy tone current over the trunk line andinterrupts, at the contacts 336,r the previously traced alternativeholding circuit for f energizing the winding of the hold relay R360. At'this point it is noted that the hold relay R350 does not immediatelyrestore, this relay being of the slow-to-release type, and is retainedin its operated position as long as the impulse relay R310 and thecontrol relay R315 are interacting,v

inthe manner previously` explained, vthereby to clear the variousregisters in the key sender 33; alsov until the'registers in the keysender 33 are cleared the send relay R345 andthe answer relay R350remain in their*operatedpositions. After the registers in the key,sender 33 have been cleared; thef'previously traced circuitfor'energizing the send relay "R345 is interrupted, thereby to cause thelatter relay to restore and interrupt, at the contacts 338, thepreviously traced circuit for energizing the answer relay R350,whereupon v the latter relayresto'res as previously explained. Also uponrestoringthe sendr relay R345 interrupts, at the contacts 341, thepreviously traced circuit for energizingv the lower'winding of thecontrol relay R315, thereby to cause the latter relay to restore andinterrupt, at the contacts 311, a further point in .the` previouslytraced "circuit for energizing the winding of the impulse relay R310,whereby both the control relay R315 and the impulse'relayRSlO occupytheir restored positions. Shortly after the impulse relay R310 restoresto interrupt,.at the contacts 313, the previously mentioned alternative1Aholding circuitfor energizing the winding of the hold relay R350, thehold relay R330, be,.-

ing of the slow-'to-release type, restores. At this time, the selectorrepeater is completely released and available for further use.

On the other hand, assuming -that the present "release is effectedsubsequent to the establishment of the completed connection between thecalling subscriber substation A in the distant exchange 1.0 and thecalled subscriber substation D in the set 'of the switching mechanism300 to be released and .returned to its normal position, in the mannerpreviously explained. Also the sets of switch springs YSSID,S3I3andS3ll, S3|2 are respectively actuated into engagement anddisengagement, as previously explained. Further in the present release,the hold relay R330 interrupts,v

at the c ontacts 336, the previously traced circuit for energizing thewinding of the switching relay R390 in series with the lower winding ofthe control relay R315, thereby to cause the switching relay R390 torestore. Upon restoring, the switching relay R390 interrupts, at thecontacts 392 and 393, the previously` traced connection between theselector repeater 55 and the trunk 36 extending to the local automaticswitch train 2| and interrupts, at the contacts 395, the previouslytraced path for applying ground potential to the control conductor C413of the trunk 36, the path for applying ground potential to the controlconductor C414 of the trunk 36 being interrupted at the contacts 321incident to the restoration of the line relay R325. At this time, theselector repeater 55 is completely released and available for furtheruse. When ground potential is removed from the control conductors C413and C414 of the trunk 36 extending to the local automatic switch train2|, the local automatic switch train 2| is released and renderedavailable for further use. At this time, when the local automatic switchtrain 2| is released the line circuit 46 individually associated withthe telephone line 42 extending to the called subscriber substation D inthe central exchange is controlled, thereby to mark the telephone line42 as idle to the switches in the local automatic switch train 2| havingaccess thereto in the event the subscriber at the called subscribersubstation D has replaced the receiver of the telephone instrumentthereat upon its associated switchhook at this time, or to lock thetelephone line 42 out of service in the event the subscriber at thecalled subscriber substation D has not replaced the receiver of thetelephone instrument thereat upon its associated switchhook at thistime.

In connection with the release of the selector repeater 55 it is notedthat, in the event the wiper set of the switching mechanism 300 is notcompletely released and actually returned to its normal positionincident to the restoration of the hold relay R330, a path is completed,at the contacts 33|, upon restoration of the hold relay R330 to applyground potential to the line conductor C2|0 of the trunk line 50, thispath extending from ground by way of the set of switch springs 53| andthe contacts 33| to the line conductor C2| 0 of the trunk line 50.Accordingly, ground potential is retained upon the line conductor C2|0of the trunk line 50 until the wiper set of the switching mechanism 300is actually returned to its normal position, thereby to actu- `ate theset of switch springs S3| into disengagement. The application of groundpotential to the line conductor C2|0 completes a circuit for energizingthe winding of the .busy relay R240 in the trunk circuit 80, thiscircuit extending from the grounded line conductor C2I0 of the switchingmechanism 300 in the selector repeater 55 is completely released andreturned to its normal position, the set of switch springs S3l| isactuated into disengagement, thereby to interrupt the previously tracedcircuit for energizing the winding of the busy relay R240. The busyrelay R240 then restores, thereby to interrupt, at the contacts 24|, thepreviously mentioned path for applying ground potential to the controlconductor C203 of the trunk 8| in order to mark the trunk 8| as idle tothe non-numerical automatic switches having access thereto.

At this point it is noted that the call initiated at the callingsubscriber substation A in the distant exchange 10 and routed therefromby way of the telephone line 1|, the non-numerical automatic switch 18,the trunk 8|, the trunk circuit 80, the trunk line 50, the selectorrepeater 55 and the trunk 35 to the first operator position 30 andanswered at the first operator position 30 by operating the connect keyK440 in the operator connecting apparatus 32, may be completed toanother subscriber substation in the distant exchange 10 instead of tothe subscriber substation D in the central exchange 20, in the mannerpreviously explained. The operation of the apparatus in the centralexchange 20 -to extend a call answered at the rst operator position 30to a subscriber substation in the distant exchange 10 is described morefully hereinafter.

Also it is noted that the call on the telephone line 1| and routed byway of the previously traced piece of apparatus to the rst operatorposition 30 and answered thereat may have been initiated on thetelephone line 1| due to the presence of a fault thereon. In otherwords, the call on the telephone line 1| answered at the rst operatorposition 30 may be a false call. After the operator at the firstoperator position 30 detects that the call routed thereto by way of theselector repeater 55 and the trunk 35 is a false call, she operates thekey sender 33, thereby to cause a single predetermined digit to beregistered in the first register 400 therein. After the single digit isregistered in the rst register 400 in the key sender 33, operation ofthe selector repeater 55 is initiated, thereby to cause the wiper set ofthe switching mechanism 300 to be driven in the vertical direction acorresponding number of steps, in the manner previously explained. Thewiper set of the switching mechanism 300 is then driven step by step inthe rotary direction until it is driven eleven steps away from itsnormal position, this level in the associated contact bank terminatingno trunks. When the wiper set of the switching mechanism 300 is thusoperated in the vertical direction the set of `switch springs S3|4 isactuated into disengagement; and when the wiper set of the switchingmechanism 300 is thus operated in the rotary direction the sets ofswitch springs S3|5 and S3|8 are actuated, the sets of switch springsS3| 0, S3|3 and S3||, S3|2 being respectively actuated intodisengagement and engagement at this time, as previously explained. Moreparticularly, the contacts 320 of the set of switch springs S3|8 areactuated into engagement, thereby to complete the previously tracedalternative holding circuit for energizing the winding of the hold relayR360. When thus energized the hold relay R360 operates, thereby tocondition the impulse relay R310 and the control relay R315 foroperation in order to insure that the various registers in the keysender 33 are cleared. Also the contacts 3|1 of the set of switchsprings S3|5 are actuated into dis-

